The right sign for "didn't" depends on the situation.
● Often the concept of "didn't" is expressed via a negative shake of the head while signing that which you didn't do or which didn't happen.
For example, to sign, "I didn't go" -- you would shake your head negatively while signing "GO."
This is sometimes written (glossed) as "PRO-1 GO-[neg]"
That "PRO-1" can be thought of as meaning "first person pronoun" which means "I or me."
● In addition to using the negative head shake you can add the "NOT" sign to your sentence.
For example: "PRO-1 NOT GO-[neg]."
● Sometimes the concept of "didn't" is incorporated into the movement of the sign. This happens with the following signs:
WANT + a reversal of orientation becomes "don't-WANT" -- which can be included in such sentences as: "PRO-3 don't-WANT GO" -- which could be interpreted as, "He (or she) didn't want to go."
KNOW + a reversal of orientation becomes "don't-KNOW" -- which can be included in such sentences as: "PRO-3 don't-KNOW HOW" -- which could be interpreted as, "He (or she) didn't know how."
LIKE + a reversal of orientation becomes "don't-LIKE"-- which can be included in such sentences as: "PRO-3 don't-LIKE I-T" -- which could be interpreted as, "He (or she) didn't like it."
● Another way the "didn't" concept might come up is in the sign for "don't-MIND." If asked if you found something annoying (BOTHER), you might reply "I don't-MIND" which could be interpreted as "I didn't mind it."